Astronomers Find 70 Planets Without Stars Floating Free in the Milky Way

This artist’s impression shows an example of a rogue planet with the Rho Ophiuchi cloud complex visible in the background. Rogue planets have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own.

The field of extrasolar planet studies continues to reveal some truly amazing things about our Universe. After decades of having just a handful of exoplanets available for study, astronomers are now working with a total of 4,884 confirmed exoplanets and another 8,288 awaiting confirmation. This number is expected to increase exponentially in the coming years as next-generation missions like the James Webb Space Telescope (JWST), Euclid, PLATO, and the Nancy Grace Roman Space Telescope (RST) reveal tens of thousands more.

In addition to learning a great deal about the types of exoplanets that are out there and what kind of stars are known to give rise to them, astronomers have also made another startling discovery. There is no shortage of exoplanets in our galaxy that don’t have a parent star. Using telescopes from around the world, a team of astronomers recently discovered 70 additional free-floating planets (FFPs), the largest sample of “Rogue Planets” discovered to date, and nearly doubling the number of FFPs available for study.

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Rogue Planets Could be Habitable

An artist's illustration of a rogue planet, dark and mysterious. Image Credit: NASA

The search for potentially habitable planets is focused on exoplanets—planets orbiting other stars—for good reason. The only planet we know of with life is Earth and sunlight fuels life here. But some estimates say there are many more rogue planets roaming through space, not bound to or warmed by any star.

Could some of them support life?

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Protoplanetary Disks Throw Out More Material Than Gets Turned Into Planets

When a young solar system gets going it’s little more than a young star and a rotating disk of debris. Accepted thinking says that the swirling debris is swept up in planet formation. But a new study says that much of the matter in the disk could face a different fate.

It may not have the honour of becoming part of a nice stable planet, orbiting placidly and reliably around its host star. Instead, it’s simply discarded. It’s ejected out of the young, still-forming solar system to spend its existence as interstellar objects or as rogue planets.

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Multiple Earth-Mass Rogue Planets Have Been Discovered Drifting Through the Milky Way

Last year we reported on how the Roman Space Telescope’s backers hoped it would be able to detect rogue planets using a technique called “microlensing”.  Now, a team led by Iain McDonald, then at the University of Manchester, beat them to the punch by finding a few examples of Earth-sized rogue planets using data from an already aging space telescope – Kepler.

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The Moons of Rogue Planets Could Have Liquid Surface Water and Thick Atmospheres. They Could be Habitable

Artist's rendering of an Earth-sized rogue planet approaching a star. Credit: Christine Pulliam (CfA)

The search for life on exoplanets takes a fairly conservative approach. It focuses on life that is similar to that of Earth. Sure, it’s quite possible that life comes in many exotic forms, and scientists have speculated about all the strange forms life might take, but the simple fact is that Earth life is the only form we currently understand. So most research focuses on life forms that, like us, are carbon based with a biology that relies on liquid water. But even with that narrow view, life could still be hiding in places we don’t expect.

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In the Far Future, Stellar Flybys Will Completely Dismantle the Solar System

A lovely artistic look at our Solar System that's definitely not to scale. Image Credit: NASA

Consumption and disintegration.

Next time you want to be the life of the party—if you’re hanging out with cool nerds that is—just drop that phrase into the conversation. And when they look at you quizzically, just say that’s the eventual fate of the Solar System.

Then adjust your cravat and take another sip of your absinthe.

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A Rogue Earth-Mass Planet Has Been Discovered Freely Floating in the Milky Way Without a Star

An artist's impression of a rogue planet. Image Credit: By - Own work, CC BY-SA 4.0,

If a solar system is a family, then some planets leave home early. Whether they want to or not. Once they’ve left the gravitational embrace of their family, they’re pretty much destined to drift through interstellar space forever, unbound to any star.

Astronomers like to call these drifters “rogue planets,” and they’re getting better at finding them. A team of astronomers have found one of these drifting rogues that’s about the same mass as Mars or Earth.

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Planetary Mass Objects Discovered in Other Galaxies

In this artist's conception, a rogue planet drifts through space. Credit: Christine Pulliam (CfA)
In this artist's conception, a rogue planet drifts through space. Credit: Christine Pulliam (CfA)

A team of researchers at the University of Oklahoma have discovered “planetary mass bodies” outside of the Milky Way. They were discovered in one gravitationally-lensed galaxy, and in one gravitationally-lensed galaxy cluster using a technique called quasar micro-lensing. According to the researchers, the planetary mass objects are either planets or primordial black holes.

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Is it a Massive Planet or a Tiny Brown Dwarf. This Object is Right at the Border Between Planet and Star

Artist's conception of SIMP J01365663+0933473, an object with 12.7 times the mass of Jupiter, but a magnetic field 200 times more powerful than Jupiter's. This object is 20 light-years from Earth. Credit: Caltech/Chuck Carter; NRAO/AUI/NSF

Rogue planets are a not-too-uncommon occurrence in our Universe. In fact, within our galaxy alone, it is estimated that there are billions of rogue planets, perhaps even more than there are stars. These objects are basically planet-mass objects that have been ejected from their respective star systems (where they formed), and now orbit the center of the Milky Way. But it is especially surprising to find one orbiting so close to our own Solar System!

In 2016, scientists detected what appeared to be either a brown dwarf or a star orbiting just 20 light years beyond our Solar System. However, using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), a team of astronomers recently concluded that it is right at the boundary between a massive planet and a brown dwarf. This, and other mysterious things about this object, represent a mystery and an opportunity to astronomers!

The study which describes their findings recently appeared the Astrophysical Journal under the title “The Strongest Magnetic Fields on the Coolest Brown Dwarfs.” The team was led by Melodie Kao – who led this study while a graduate student at Caltech, and is now a Hubble Postdoctoral Fellow at Arizona State University – and included members from Arizona State University, the University of Colorado Boulder, the California Institute of Technology, and the University of California San Diego.

To summarize, brown dwarfs are objects that are too massive to be considered planets, but not massive enough to become stars. Originally, such objects were not thought to emit radio waves, but in 2001, a team using the VLA discovered a brown dwarf that exhibited both strong radio emissions and magnetic activity. Ongoing observations also revealed that some brown dwarfs have strong auroras, similar to the gas giants in our Solar System.

This particular object, known as SIMP J01365663+0933473, was first discovered in 2016 by the Caltech team as one of five brown dwarfs. This survey was part of VLA study to gain new knowledge about magnetic fields and the mechanisms by which the coolest astronomical objects can produce strong radio emissions. Since brown dwarfs are incredibly difficult to measure, the object was initially though to be too old and too massive to be a brown dwarf.

However, last year, an independent team of scientists discovered that SIMP J01365663+0933473 was part of a very young group of stars whose age, size and mass indicated that it was likely to be a free-floating (aka. rogue) planet rather than a star. In short, the object was determined to be 200 million years old, 1.22 times the radius of Jupiter and 12.7 times its mass.

It was also estimated to have a surface temperature of about 825 °C (1500 °F) – compared to the Sun’s, which is 5,500 °C (9932 °F). Simultaneously, the Caltech team that originally detected its radio emission in 2016 observed it again in a new study at even higher radio frequencies. From this, they confirmed that its magnetic field was even stronger than first measured, roughly 200 times stronger than Jupiter’s.

As Dr. Kao explained in a recent NRAO press release, this all presents a rather mysterious find:

“This object is right at the boundary between a planet and a brown dwarf, or ‘failed star,’ and is giving us some surprises that can potentially help us understand magnetic processes on both stars and planets… When it was announced that SIMP J01365663+0933473 had a mass near the deuterium-burning limit, I had just finished analyzing its newest VLA data.”

In short, the VLA observations provided both the first radio detection and the first measurement of the magnetic field of a planetary-mass object beyond our Solar System. The presence of a such a strong magnetic field represents a huge challenge to astronomers’ understanding of the dynamo mechanisms that create magnetic fields in brown dwarfs, not to mention the mystery of what drives their auroras.

Ever since brown dwarfs were observed to have auroral activity, scientists have wondered what could be powering them. On Earth, as with Jupiter and the other Solar planets that experience them, aurorae are the result of solar wind interacting with a planet’s magnetic field. But in the case of brown dwarfs, which have no parent star, some other mechanism must be involved. As Kao explained:

“This particular object is exciting because studying its magnetic dynamo mechanisms can give us new insights on how the same type of mechanisms can operate in extrasolar planets — planets beyond our Solar System. We think these mechanisms can work not only in brown dwarfs, but also in both gas giant and terrestrial planets.”

An artist’s conception of a T-type brown dwarf. Credit: Wikipedia Commons/Tyrogthekreeper

Kao and her team think that one possibility is that this object has an orbiting planet or moon that is interacting with its magnetic field, similar to what happens between Jupiter and its moon Io. Given its proximity to our Solar System, scientists will have the opportunity to address this and other questions, and to learn a great deal about the mechanics that power gas giants and brown dwarfs.

Studying this object will also help astronomers place more accurate constraints on the dividing line between massive planets and brown dwards. And last, but not least, it also presents new opportunities as far exoplanet research is concerned. As Gregg Hallinan, who was Dr. Kao’s advisor and a co-author on the Caltech study, explained:

“Detecting SIMP J01365663+0933473 with the VLA through its auroral radio emission also means that we may have a new way of detecting exoplanets, including the elusive rogue ones not orbiting a parent star.”

Between finding planets that orbit distant stars to planetary-mass objects that orbit the center of the Milky Way, astronomers are making exciting discoveries that are pushing the boundaries of what we know about planetary formation and the different types that can exist. And with next-generation instruments coming online, they plan to learn a great deal more!

Further Reading: NRAO, The Astrophysical Journal

Rogue Planets Could Form On Their Own in Interstellar Space

Astronomers have found that tiny, round, dark clouds called globulettes have the right characteristics to form free-floating planets. The graph shows the spectrum of one of the globulettes taken at the 20-metre telescope at Onsala Space Observatory. Radio waves from molecules of carbon monoxide (13CO) give information on the mass and structure of these clouds. ESO/M. Mäkelä.

Free-floating rogue planets are intriguing objects. These planet-sized bodies adrift in interstellar space were predicted to exist in 1998, and since 2011 several orphan worlds have finally been detected. The leading theory on how these nomadic planets came to exist is that they were they ejected from their parent star system. But new research shows that there are places in interstellar space that might have the right conditions to form planets — with no parent star required.

Astronomers from Sweden and Finland have found tiny, round, cold clouds in space that may allow planets to form within, all on their own. In a sense, planets could be born free.
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